REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Utility	$ 195,729	$ 219,623
Nonutility	258,576	395,413
Total operating revenues	454,305	615,036
Depreciation and amortization	27,362	24,637
Interest income	669	186
Interest expense, net of capitalized interest	19,786	16,070
Income tax provision (benefit)	17,441	16,471
Equity in earnings of affiliates	2,675	3,389
Net financial earnings (loss)	44,657	34,931
Capital expenditures	109,880	126,183
Investments in equity investees	286	509
Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues	444,680	605,322
Depreciation and amortization	27,284	24,843
Interest income	776	841
Interest expense, net of capitalized interest	18,670	16,372
Income tax provision (benefit)	18,049	16,255
Net financial earnings (loss)	44,201	33,559
Capital expenditures	109,194	126,057
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Utility	195,729	219,623
Total operating revenues	195,729	219,623
Depreciation and amortization	19,169	16,817
Interest income	82	107
Interest expense, net of capitalized interest	8,974	7,832
Income tax provision (benefit)	8,367	8,635
Net financial earnings (loss)	49,467	43,856
Capital expenditures	79,246	77,797
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Nonutility	6,370	6,212
Total operating revenues	6,370	6,212
Depreciation and amortization	5,433	6,316
Interest expense, net of capitalized interest	5,034	4,492
Income tax provision (benefit)	(3,086)	(3,834)
Net financial earnings (loss)	(10,274)	(8,179)
Capital expenditures	22,335	45,699
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	227,349	368,304
Total operating revenues	227,349	368,304
Depreciation and amortization	42	29
Interest income	0	37
Interest expense, net of capitalized interest	680	1,226
Income tax provision (benefit)	12,122	10,752
Net financial earnings (loss)	1,500	(5,122)
Operating Segments | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	12,447	8,405
Total operating revenues	12,447	8,405
Depreciation and amortization	2,640	1,681
Interest income	694	697
Interest expense, net of capitalized interest	3,982	2,822
Income tax provision (benefit)	646	702
Equity in earnings of affiliates	3,193	3,664
Net financial earnings (loss)	3,508	3,004
Capital expenditures	7,613	2,561
Investments in equity investees	286	509
Intercompany
Segment Reporting Information [Line Items]
Nonutility	167	415
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility	2,128	2,111
Intercompany | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	657	667
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility	12,410	12,492
Total operating revenues	12,410	12,492
Depreciation and amortization	260	246
Interest income	132	491
Interest expense, net of capitalized interest	1,116	272
Income tax provision (benefit)	118	219
Net financial earnings (loss)	(62)	1,109
Capital expenditures	686	126
Eliminations
Segment Reporting Information [Line Items]
Nonutility	(2,952)	(3,193)
Depreciation and amortization	(182)	(452)
Interest income	(239)	(1,146)
Interest expense, net of capitalized interest	0	(574)
Income tax provision (benefit)	(726)	(3)
Equity in earnings of affiliates	(518)	(275)
Net financial earnings (loss)	$ 518	$ 263